When you download a 3DS game as a .cia file (often from custom firmware/homebrew communities), it does not include the official update patches. To get bug fixes, performance improvements, and online connectivity, you must install the Update manually. A "CIA" update file is essentially the digital package Nintendo would have pushed through the eShop, repackaged for offline installation.
Nintendo released two updates for Ultra Sun/Moon: v1.1 (minor bug fixes) and v1.2 (major content and online adjustments). Most modern ROM hacks (like Ultra Sun & Moon – Darthion’s Edition ) require base v1.2 to function. Pokemon Ultra Sun- Update 1.2 3DS -WORLD- CIA -...